1. Field of the Invention
The present invention generally relates to a navigation apparatus for a moving object. More specifically, the present invention is directed to a navigation apparatus for a moving object capable of setting an optimum scale of a map displayed on a display unit of the moving object, depending upon moving conditions of the moving object, e.g., moving vehicles or the like. These moving conditions involve, for instance, a distance between a present position of a moving vehicle and a place to which a moving vehicle is directed; a moving velocity of a moving object; and a variation in a steering angle of a moving object and the like.
2. Description of the Prior Art
A great attention is given to a GPS navigation apparatus that is useful to confirm and/or decide a present position and a moving velocity of various types of moving objects such as ships, aircrafts, automobiles by transmitting electromagnetic waves toward these moving objects from a plurality of artificial satellites. It should be understood that the above-described GPS navigation apparatus implies the Global Positioning System where the present position of the moving object can be recognized by receiving the electromagnetic wave transmitted from a plurality of artificial satellites belonging to the GPS navigation system.
As is known in the art, the navigation operation utilizing such a GPS navigation apparatus is normally carried out by receiving the electromagnetic waves transmitted from more than three artificial satellites These electromagnetic waves transmitted from a plurality of artificial satellites are simultaneously received at the side of the moving object, a predetermined correction is performed for a time shift based upon a difference in time precision between a timer device employed in the moving object and timer devices employed in a plurality of artificial satellites, and thereafter the present position of the moving object is displayed by the proper display means In this case, the required map information is displayed on the above-described display means being superimposed on the information of the above-described present position.
As the above-described navigation apparatuses for the various types of the moving objects, a so-called "self-contained" type navigation apparatus is known. Such a sort of the self-contained type navigation apparatus is different from the above-described GPS navigation apparatus, and is characterized in that the present position of the moving object can be confirmed based upon only the data which have been acquired by the moving object itself independent upon the external data such as the navigating electromagnetic waves from the artificial satellites.
FIG. 1 is a schematic block diagram of the above-described conventional navigation apparatus. In FIG. 1, reference numeral 3 denotes an antenna for receiving the electromagnetic waves transmitted from the satellites. An output side of the antenna 3 is connected to a receiver unit 4. Reference numeral 1 indicates a sensor for a drive distance, and reference numeral 2 represents an azimuth sensor, which are connected to the output side of the receiver unit 4, and also to a position detecting unit 5. An output side of the position detecting unit 5 is connected to a data processing unit 8. Also a key input unit 6, a map data memory unit 7 and a display unit 9 are connected to the above-described data processing unit 8.
An operation of this navigation apparatus will now be described. An operator for a moving object such as a vehicle depresses, for example, a starting key mounted on the key input unit 6 so as to initialize the above-described navigation apparatus for the moving object. Subsequently, a function key such as a selection key is depressed, so that either GPS type navigation function, or self-contained type navigation function is selected. Assuming now that the former navigation function is selected, both the drive distance sensor 1 and azimuth sensor 2 are electrically separated from the position detecting unit 5 by actuating a mechanical switch or the like (not shown), with the result that the present position and moving direction of the moving object are recognized or decided based upon only the electromagnetic waves received via the antenna 3 from the artificial satellites. When, on the other hand, the GPS navigation function cannot be selected due to existence of various interfering objects, the self-contained type navigation function is selected. Accordingly, the present position and moving direction of the moving object are confirmed and decided based upon only the data acquired from the drive distance sensor 1 and azimuth sensor, 2.
In such a conventional navigation apparatus, only the map illustrating the present position of the moving object is merely displayed on the display unit 9, and since the display scale is fixed on this display unit 9, the following drawback may be provided. That is, as the destination place to which the moving object is directed is located far from the present position, for instance, both positions cannot be observed at one time by utilizing a single display screen of the display unit 9. In such a case, an operation is required to properly change the map illustrating the present position of the moving object and the map illustrating the destination place to which the moving object is directed. Moreover, such a map changing operation is required in conjunction with the moving operation of the moving object. As a result, there is a risk that the safety driving operation of the moving object may not be expected.
In addition, since the display scale is fixed regardless the moving velocity of the moving object in the conventional navigation apparatus, the fine moving paths are simply displayed on the display unit 9 even if, for instance, the moving object is moving at the higher velocity. As a consequence, it is difficult that the operator of the moving object can surely observe the display screen under the high-speed movement. Furthermore, since such a map observation must be performed in conjunction with the driving operation of the moving object, the satisfactory drive operation of the moving object may not be achieved.
Also in the conventional navigation apparatus, since the display scale is fixed regardless of the variations in the steering angle occurring in the movement of the moving object, it is difficult for the operator of the moving object to observe the display screen on which the fine moving paths are merely displayed under the following conditions. That is, even when, for example, the moving object is required to be quickly turned at the crossing on the moving path during which the precise driving operation of the moving object must be required, the operator is required to observe such a fine moving path displayed on the display screen. As a consequence, the above-explained risks may be induced in such a conventional navigation apparatus